The operation of high-pressure discharge lamps using electronic ballasts is conventional per se. Such ballasts contain converters, often half-bridge converters having two switching transistors and full-bridge converters having four switching transistors. During continuous operation of the lamp, these converters produce, in simple terms, DC voltage supply powers for the lamp which alternate in terms of their polarity at a low frequency. In this case, with pure DC operation, interference phenomena occurring in the lamp as a result of the asymmetry are avoided, but at the same time higher frequencies which are likewise interference are largely kept away from the lamp.
It is also known to measure the lamp current in the case of such ballasts, for example in order to supply a safety shutdown, in the event of specific threshold values being exceeded or undershot, or a regulating circuit for the purpose of regulating the lamp current or the lamp power with a corresponding signal. During operation of the converter, switching phases of alternating polarity of the currents through the switching transistors result, such that various solutions are documented in the prior art for dealing with the resulting polarity change in the measured current signal.